1. Field of the Invention
The present invention relates to a liquid detection device for detecting the presence or absence of a liquid in a liquid supply mechanism which is equipped with a storage member for temporarily storing a liquid to be supplied and a liquid tank for replenishing the storage member with the liquid. More particularly, the invention relates to a device that may be advantageously used for detecting the presence or absence of an offset prevention oil in a fusing unit provided in an electrophotographic apparatus.
2. Description of the Related Art
In a fusing unit provided in an electrophotographic apparatus such as an electrophotographic printer or electrophotographic copier, oil is applied to a roller to prevent offset, a phenomenon in which toner sticks to the roller. The oil supply mechanism provided for this purpose comprises an impregnated member formed from a porous material, such as a felt or sponge, and a detachable oil tank for replenishing the impregnated member with oil.
In the prior art, when detecting the presence or absence of oil remaining in such an oil supply mechanism, it has not been possible to detect the oil remaining in the impregnated member simultaneously with the oil remaining in the tank, and separate detection mechanisms have had to be provided if the amounts of oil remaining in both are to be detected. Furthermore, since it is difficult to detect the oil remaining in the impregnated member, it has been widely practiced to only detect the oil remaining in the tank and relay on guesswork about the amount of oil remaining in the impregnated member.
However, in an apparatus that issues a tank replacement request only by detecting the presence or absence of oil remaining in the tank, there can occur cases where the tank is replaced when the impregnated member is saturated with oil. In such cases, oil may be excessively supplied to the impregnated member. Conversely, when there is oil remaining in the tank, but no oil remaining in the impregnated member, sufficient oil may not be applied.
On the other hand, in an apparatus that is equipped with oil detection mechanisms for both the impregnated member and tank, and that issues a tank replacement request by detecting both the impregnated member and tank being depleted of oil, there arises the problem that not only the cost but also the complexity of control increases.
The present invention has been devised in view of the above problems, and an object of the invention is to provide a low-cost liquid detection device wherein, in a liquid supply mechanism equipped with a storage member for temporarily storing a liquid to be supplied and a liquid tank for replenishing the storage member with the liquid, a condition in which both the storage member and the tank have been depleted of the liquid and a condition in which there is liquid remaining in at least either the storage member or the tank can be easily discriminated using a single mechanism.
To achieve the above object, according to a first aspect of the invention, there is provided a liquid detection device for detecting the presence or absence of a liquid, the device equipped with a storage member for temporarily storing the liquid for supply and a liquid tank for replenishing the storage member with the liquid, the device comprising: a prism for forming a light path, having at least a first side which, when there is no liquid remaining in the liquid tank, reflects incident light into the prism and, when there is the liquid remaining in the liquid tank, lets the incident light pass therethrough into the liquid, and a second side which, when there is no liquid remaining in the storage member, reflects incident light into the prism and, when there is the liquid remaining in the storage member, lets the incident light pass therethrough into the liquid; light emitting means for emitting light into the prism; and light receiving means disposed in such a position as to be able to receive light that was emitted into the prism, reflected at the first side or the second side, and passed through the prism.
In the liquid detection device having the above construction, when there is liquid remaining in the liquid tank, the light emitted from the light emitting means into the prism is passed into the liquid without being reflected at the first face of the prism, and therefore, does not reach the light receiving means. Likewise, when there is liquid remaining in the storage member, the emitted light is passed into the liquid without being reflected at the second face of the prism, and therefore, does not reach the light receiving means. On the other hand, when there is no liquid remaining in either the liquid tank or the storage member, the emitted light is reflected at the first face or the second face and reaches the light receiving means. Accordingly, when light is detected by the light receiving means, this state can be interpreted to mean that the amount of remaining liquid is low and the tank must be replaced, and when light is not detected by the light receiving means, this state can be interpreted to mean that a sufficient amount of liquid remains and there is no need to replace the tank.
Preferably, according to the present invention, the liquid tank is detachable from the storage member, the prism is mounted in the liquid tank, and the light receiving means is disposed in such a position as to be able to directly receive the light from the light emitting means when the prism does not exist. In this device, when the liquid tank is not mounted, the light receiving means directly receives the light emitted from the light emitting means, which is equivalent to the condition in which neither the liquid tank nor the storage member contains oil.
Preferably, according to the present invention, the liquid detection device is used as a device for detecting the presence or absence of an offset prevention oil in a fusing unit provided in an electrophotographic apparatus.
According to the present invention, when the liquid detection device is used in a fusing unit provided in an electrophotographic apparatus, preferably the shape of the prism and the locations of the light emitting means and the light receiving means are determined so that the light emitting means and the light receiving means are kept away from a high temperature area near a fusing heat roller. In this liquid device apparatus, the light emitting means and the light receiving means can be prevented from being exposed to high temperatures, and its performance prevented from degrading.
Furthermore, according to the present invention, there is provided an electrophotographic apparatus comprising a fusing unit that is equipped with the above liquid detection device as a device for detecting the presence or absence of an offset prevention oil.